hurricanes

tropical cyclone

• large, spiral-shaped storm

• originates over warm tropical ocean waters

• rotation around a low-pressure centre

types of tropical cyclones (based on geography)

• hurricane - North Atlantic or eastern Pacific Ocean

• typhoon - northwestern Pacific Ocean

• cyclone - Indian Ocean or Australia

hurricane progression

• tropical disturbance → tropical depression → tropical storm → hurricane

• changes w/ increasing wind speeds

Saffir-Simpson Scale

• communicates intensity of storm based on max sustained wind speed

• does not include amount of rain produced or damage caused

anatomy of hurricane: eye

• downward-tapering vertical cylinder

• calm, clear air

• centre of hurricane

anatomy of hurricane: eye wall

ring of dense, rapidly swirling clouds

anatomy of hurricane: spiral rainbands

• bands of clouds that spiral outward from eyewall

• torrential downpours come from base

• little-no rain in gaps b/w rainbands

hurricane formation

• develop only over tropical waters w/ temp above 26°C to a depth of at least 60 m

• heat (thermal energy) required to drive airflow

• only warm ocean waters can provide enough heat to accelerate winds to hurricane speeds

hurricane season

• time when water becomes warm enough to fuel tropical storms

• Atlantic & E Pacific = June-Nov

• W Pacific = July-Oct

lifting mechanisms

• thunderstorms form from air convergence, where faster/slower or opposing air masses merge

• convergence forces air upward; if moist air rises and cools, condensation releases latent heat

• this heat makes the air unstable, causing it to rise higher and form thunderstorms

• in the W Pacific and Indian Ocean, convergence occurs along the ITCZ where SW trade winds (N Hemisphere) meet NW trade winds (S Hemisphere)

evolution of tropical disturbance into hurricane can only happen if…

1. storm must have uninterrupted supply of warm, evaporating seawater

2. storm must develop in a region where high-altitude winds are not strong enough for wind shear to tear apart rotation

hurricane can stop for any 3 reasons

1. moves higher altitudes (cooler surface water & thinner troposphere)

2. drifts over land (supply of evaporating water decreases & the wind slows)

3. drifts into a region of strong high-altitude winds (wind shear disrupts the cyclonic flow)

hurricane tracks

• path that follows the hurricanes center over time plotted on a map

• Coriolis force is very weak at the equator, for that reason hurricanes never form on, or cross the equator 

hurricane damage: wind damage

• category 1 (weakest) = 119 km/hour

• category 5 (strongest) = 252 km/hour

• damage depends on intensity & duration of winds

• wind applies dynamic pressure to any object it impacts

hurricane damage: storm surge

• rise of sea level due to winds

• produces dome-like mound of ocean water that rises above mean sea level

• storm surge reaches shore → inundation of land

• can be amplified if reach shore during high tide or when it enters bays & estuaries

hurricane damage: wave damage

• ships in water

• waves as high as 28 m

hurricane damage: rain, inland flooding, landslides

• flooding due to torrential rains

• in steep/unstable terrain, soil/sediment become saturated → triggers mudslides & debris flows

hurricane damage mitigation

• hurricane tracks monitored by NASA, National Hurricane Centre, National Weather Services

• no computer model can perfectly predict future track, size or strength of hurricane

• at least 48 hrs before landfall, NHC will issue hurricane watch

• areas within 36 hrs will receive warning

in a hurricane warning people are told to…

• monitor the storm

• secure property

• evacuate

• shelter in place

Hurricane Maria

• Puerto Rico

• thousands of homes destroyed, no electrical grid

• slow to no response

scientific evidence related to climate change

• glaciers have lost more mass than they have gained

• negative mass balance

Peru

• 3 main geographic regions

  • coast, highlands, jungle

• 8th in renewable fresh water resources

• Pacific Drainage Basin

  • 1.8% of Peru’s water

  • 65% of Peru’s population

Rio Santa Basin (Peru)

• 1.7 million population

• semi-arid climate with high seasonal precipitation

• economy based on agriculture, mining, fishing & labor 

• contributes to ~5% of country’s hydroelectric generation

• water comprised of

  • precipitation catchment, glacier run off, groundwater discharge

climate change

• increasing temperature

• variable precipitation

climate change: glaciers

• glacier run off

  • responsible for 10-20% of total discharge

  • up to 66% during dry season

• once all glaciers melt

  • annual discharge lowered by 2-30%

  • decrease of 30% during dry season

glacial landforms: latero-frontal moraines

• landforms generated at margins of glaciers

• steep sides, often ice cored, prone to slope failure

• barriers to drainage → impound lakes receiving glacial melt water

• if barrier breached/overtopped → glacial lake outburst floods (GLOF)

hydro-sociology

• hydrological factors →

  • glacier meltwater + hydrological processes → hydrologic processes (e.g. climate change, gw storage)

• ← available water sources →

  • function of hydraulic & societal factors

• ← social factors

  • human variables: political & economic development, governance, technology & engineering, land use, societal response

  • values, knowledge, culture

  • water resource demand

water security

the availability of an acceptable quantity and quality of water for health, livelihoods, ecosystems and production, coupled with an acceptable level of water-related risks to people, environments and economies

glacial sedimentology & geomorphology

• 10% of the world’s population lives in areas that will be prone to GLOFs in decades to come

• Western Canadian Rockies have experienced GLOFs in the past & will see an increase in events in future